Monday, March 09, 2009

As with many a key sabermetric tenet, Bill James is responsible for introducing the idea that ballplayers, or at least hitters, reach their peak value at the age of 27. In fact, it was a serendipitous 27 years ago, in the 1982 Baseball Abstract, that James first presented his research supporting this conclusion, thus contradicting the then-prevailing wisdom that ballplayers peak between the ages of 28 and 32.

While you wouldn't know it to see the way certain front offices function when signing over-the-hill hitters, this particular bit of James' wisdom has withstood the test of time, and has even undergone some expansion. Using more advanced valuation methods, Nate Silver has found that players peak between the ages of 25 and 29, generally cresting at 26 and 27, with some understandable variations by positions. Speed-based players, like middle infielders and center fielders, tend toward the earlier side of that range.

Baseball fans like their rules of thumb simple, however, and focusing on hitters about to enter their age-27 seasons is particularly popular in the fantasy realm. Although this year's "Class of 27" isn't full of marquee names whose eye-popping numbers match those of 25-year-old Hanley Ramirez, 26-year-olds David Wright and Jose Reyes, or 29-year-old Albert Pujols, it's worth a gander.

For the list I ranked the nine players with the highest Equivalent Average forecasts, then interpolated between the various PECOTA percentile forecasts to estimate the chances they're reach .300 EqAs and reach their career EqAs. Playing to the home crowd, here's what I had to say about the Dodgers' Andre Ethier (third on the list) and the Brewers' Corey Hart (seventh):

Andre Ethier, Dodgers RF (.292/.368/.464, .292 EqA, Reach .300: 36%, Reach .293: 50%)Perhaps no Dodger should be smiling as widely as Ethier after Wednesday's Manny Ramirez signing, as it returns the player whose arrival coincided with Ethier's scorching .368/.448/.649 performance over the final two months, less likely due to any mythical protection effect than to the end of Joe Torre's dickering with the lineup's Pierres and Joneses at Ethier's expense. Ethier forecasts to have the highest EqOBP of any player here (.372), and assuming that he again hits ahead of Ramirez, that will put extra runs on the board for L.A.

Corey Hart, Brewers RF (.289/.343/.494, .286 EqA, Reach .300: 28%, Reach .277: 59%)Hart went from being the second most valuable Brewer in 2007 to a basket case this past year, hitting just .252/.275/.452 from June onward, and hacking his way into an 0-1 hole more often than any other player. PECOTA believes he can recover his plate discipline, and it gives him about a 25 percent chance at 25 home runs and 25 steals.

As a side note, I remember the 1982 Abstract fondly, having borrowed the first mass market edition from a friend for the better part of a summer and gone nuts with my pocket calculator figuring out Runs Created for the players on the Salt Lake Gulls. I was 12 at the time, the young whippersnapper you see in the Little League photo on the site banner. I eventually returned that copy, and never tried to fill that hole in my collection until I recently won the bidding for a copy on eBay. Can't wait to get my hands on that one again; it really blew my mind, and it remains one of the most important baseball books in the field of sabermetrics.